Organic conducting polymers and organic electroactive polymers have been used to make electrochromic devices. However, there remains a need for elastomeric electrochromic polymers that are easily manufactured, exhibit desired electrochromic characteristics, can be covalently bonded to an electrode, have a long life-time, and can be used in an all solid-state electrochromic system.
Electrochromic systems based on polymeric electrolytes are known [B. Scrosati, J. Electrochem Soc., 1989, 136, 2774]. One example comprises polyethylene oxide and lithium salts. However, the disclosed system requires a relatively high temperature of operation (i.e., about 100° C.). This is because the conductivity is a property of the amorphous, elastomeric phase, and the transition from the crystalline to amorphous state for the PEO/Li complexes occurs above about 60° C.
Elastomer electrolytes blended with inorganic or organic chromophores have been reported [E. A. R. Duek, et al., Adv. Materials 5, 650, 1993].
World Patent Publication WO/2006/008776 discloses electrochromic compositions obtained by blending polymers with electrochromic molecules and placticizers.
Blends of conducting polymers with thermoplastics or elastomers to produce materials that exhibit the electrochromic properties of the conducting polymers are also known. For example, W. A. Gazotti et al. have disclosed solid state devices using two optically complementary electrochromic blends deposited on transparent electrodes (ITO) and a polymeric electrolyte [Advanced Materials, 1998, 10, no 18, p 1522-1525].
Improvements are desirable, however, in uniformity, consistency, efficiency, and durability.